1. Field of the Invention
The present invention relates to an automatic transmission for a vehicle, such as a hydrostatic continuously variable transmission in which a fixed capacity hydraulic pump and a variable capacity hydraulic motor are connected by a hydraulic closed circuit. More particularly, the present invention relates to a method controlling the variable transmission and a sub-gear transmission.
2. Description of the Relevant Art
Hydrostatic continuously variable transmissions are well-known. Such transmissions are applied to various vehicles, such as motorcycles. Japanese Patent No. 2527199 describes a control method for a hydrostatic continuously variable transmission, in which an actual rotation speed (Ne) of a crankshaft, or the like, is compared with a target rotational speed (Ne), which has been determined in accordance with predetermined conditions. Output power is controlled by adjusting an inclination angle of a movable swash plate, based upon the comparison.
Japanese Patent Laid-Open No. Hei 8-82354 discloses a control method for a continuously variable transmission in which a gear ratio is controlled in a step-by-step manner, as in a manual multi-step transmission (this method is called xe2x80x9cmulti-stage variable transmission controlxe2x80x9d).
When a throttle is closed during downhill driving, for example, the foregoing continuously variable transmission holds the gear ratio at a value immediately prior to downhill driving in order that the vehicle can smoothly decelerate.
Japanese Patent Laid-open No. Hei. 9-203460 discloses a gear control apparatus for a continuously variable transmission capable of multi-stage gear control. The apparatus is provided with a mode switch, and the multi-stage transmission control starts upon setting of the mode switch to multi-stage gear mode, and the gear control similar to a manual multi-stage transmission starts operating upon operation of a shift lever to select a predetermined target gear ratio with a prescribed number of stages.
The prior art suffers several drawbacks. In reverse driving utilizing the transmission apparatus, when the sub transmission lever of the driving range switch is set to the R range, being a reverse position, the gear position detection switch in the sub transmission case activates in co-operation with the sub transmission lever and detects a reverse traveling condition of the vehicle, and in the event that reverse driving is detected, the gear ratio is fixed as far as possible on the LOW side (e.g., with an output/input transmission ratio relatively low).
With the structure of the related art mentioned above, if the sub transmission lever is switched to the R range while the gear position detect switch is damaged, it will indicate the D or L range despite it actually being in the reverse driving position, the transmission cannot determine the reverse driving state, and in the event that the automatic gear mode is selected, the gear ratio may set to the TOP side and the vehicle may be accelerated unnecessarily and unwantedly. Also, in the event that stepped gear mode is selected, the gear ratio may be changed by the operation of the shift switch and the vehicle body may be accelerated too much. Therefore, there exists a need in the art for a highly reliable reverse control method, which functions even in the event of damage to the gear position detect switch.
It is an object of the present invention to solve one or more of the drawbacks associated with the background art.
It is a further object of the present invention to provide a highly reliable reverse control method, which functions even in the event of damage to the gear position detect switch.
A first aspect of the present invention concerns a transmission control method for controlling a transmission having a continuously variable transmission and a sub gear transmission arranged in series. A gear position detect switch is provided on the sub gear transmission. A reverse position detect switch is provided on a side of a change lever of the sub gear transmission. When both a gear position detect switch signal and a reverse position detect switch signal detect a reverse state, a reverse travel state is determined and a reverse control method is executed.
A second aspect of the present invention concerns a transmission control method for controlling a transmission having a continuously variable transmission and a sub gear transmission arranged in series. A gear position detect switch is provided on the sub gear transmission. A reverse position detect switch is provided on a side of a change lever of the sub gear transmission. When either one of a gear position detect switch signal or a reverse position detect switch signal detect a reverse state, the engine speed is controlled so that a specified engine speed is not exceeded.
With the method disclosed in the first aspect of the invention, a reverse driving state will be determined and reverse control will be performed only in the event that both of a gear position detect switch equipped on the sub gear transmission and the reverse position detect switch on the sub transmission lever detect the reverse driving state. The reverse control will not start in the case where either of the gear position detect switch or the reverse position detect switch is damaged, so that acceleration in the event of reverse driving can be prevented. Therefore it is effective in the event of damage to the gear position detect switch, and is possible to provide highly reliable reverse control.
With the method disclosed in the second aspect of the invention, engine speed will be controlled so as not to exceed the prescribed engine speed in the event that only one of the gear position detect switch equipped on the sub gear transmission and the reverse position detect switch on the sub transmission lever detect the reverse driving state. In a case where the sub transmission lever is shifted to a reverse position, and the reverse position detect switch detects the reverse driving state, and at the same time where the gear position detect switch is damaged and indicates the gear ratio on the forward side, the acceleration in the event of reverse driving can be prevented. Therefore it is also possible to provide highly reliable reverse control.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.